1. Field of the Invention
The present invention relates to an acoustic control system and a double talk control method thereof, and more particularly to an acoustic echo control system and a double talk control method thereof for interrupting an operation of an adaptive filter for removing acoustic echoes. In a double talk by detecting a double talk and a change of an echo path without time delay.
2. Description of the Prior Art
A hand-free communication system which does not apply a hand-set is applied to various fields such as a teleconference system, a speaker phone, etc. in order to promote convenience and stability of a speaker. Further in some countries, telephones installed in vehicles should legally follow the hand-free communication system for traffic safety.
However, in the hand-free communication system, acoustic echoes are generated though a path among a speaker, a space wherein a speaker is located and a microphone and thus communication quality is deteriorated. Accordingly, there is required an acoustic echo control system that removes the acoustic echoes. An echo controller which applies an echo removing system solves a half-duplex communication, the problem of an echo controller which applies an echo suppression system, and thus a full-duplex communication becomes possible with that controller.
In addition, since characteristics of the acoustic echoes are varied in accordance with a time change, the acoustic echo control system applies an adaptive digital filter and differently operates in accordance with a communication condition. Specifically, since coefficient radiation may be incurred when performing coefficient adaption of the adaptive digital filter in a double talk section in which speakers simultaneously talk, a double talk detecting operation is required to prevent the coefficient radiation.
To remove such echoes, although the adaptive digital filler is applied, the filter coefficient radiation in the double talk should be prevented. Accordingly, in order to achieve the double talk detection which is required according to the necessity of preventing the coefficient radiation, there has been introduced a method which applies a method of comparing sizes of signals and a method of using correlation.
An echo path may changed due to increase of a speaker volume, movement of the speaker or door opening/closing. However, with the above methods the double talk can be detected, but the double talk generation and the echo path change can not be distinguished. Furthermore, the above methods have a tendency to stick to an operation system which is not suitable for the acoustic echo control system.
For example, according to U.S. Pat. No. 5,136,577, there is introduced a method, suitable for the acoustic echo controller, which is capable of adapting a filter coefficient and discriminating the change of the double talk from the change of the echo channel. The above method applies a value of echo return loss enhancement (ERLE).
However, the problem of the conventional method is that since the value of ERLE is changed even in accordance with size of an input signal, when an actual signal is applied, an erroneous detection of double talk may be caused by which the value of ERLE is frequently changed although there is no change of the double talk or the echo channel. Thus, the conventional method is not suitable to be embodied into an actual system.